The present invention is directed to a process for removing toxic sulfur-containing compounds, ammonia, oil and grease from an aqueous solution.
A common by-product of petroleum processing is wastewater contaminated with toxic sulfur-containing compounds, ammonia, oil and grease. This contamination arises through sulfur removal measures made in the refining process. This removal is essential to minimize the sulfur that remains in the refined petroleum fuel because of the resulting sulfur dioxide that is produced upon the eventual combustion of the product. Sulfur dioxide is problematic in this sense as it is a major precursor to acidic precipitation. However, the sulfur that has been isolated through the washing process remains in a wastewater solution.
With respect to sulfur removal in petroleum processing, an aqueous washing process is used to remove reduced sulfur compounds that are naturally present in crude oil. This washing process, which is well known to those skilled in the art, involves contacting the crude petroleum product with water and then by adding ammonia to the solution at a later stage. Through this process, the sulfur, which is usually in the form of hydrogen sulfide or thiosulfate, becomes extracted from the crude petroleum product. However, oil and grease become unavoidably introduced into the system by virtue of the washing process. Hence, the aqueous solution which serves as the basis for the present invention becomes generated.
The usual course of action is to treat the wastewater by-product as a toxic substance. The wastewater is toxic because of the hydrogen sulfide and other reduced sulfur compounds that are present. These compounds have the potential to inhibit cellular electron transport systems that are vital to respiration. Hence, such compounds can be deadly.
Unfortunately, the current methodology used in treating these toxic solutions is somewhat problematic. Not only is the solution toxic because of the hydrogen sulfide present in the aqueous solution, the solution is further contaminated because of the ammonia, oil and grease that are also present. Furthermore, the solution usually has a high pH of approximately 12.1 and is quite caustic in nature.
Accordingly, each toxic aspect of the solution must be treated separately. Currently, these solutions are treated in vapor-tight holding tanks where the solutions are held for a number of days and are subjected to numerous stripping procedures where the more volatile components of the solution are separated. In addition, the solution remains at a very high pH and cannot readily be disposed through traditional industrial sewage systems without first reducing the pH to more acceptable levels. Likewise, the chemical contaminants that remain in solution must undergo further chemical treatments so as to eliminate the toxic nature of these solutions.
Moreover, treating these solutions as toxic substances is extremely costly and requires great care in maintaining toxic effluent limitations. Both Federal and State laws are in effect that place numerous restrictions and procedures with respect to the discharge of toxic wastewater. Under these statutory provisions, industrial dischargers of toxic wastewater may be required to use the best-available technology in treating the solutions, regardless of cost effectiveness. Furthermore, failure to comply with statutory effluent limitations can subject an industrial discharger to private civil suits as well as injunctions, fines, and criminal penalties under state and federal enforcement provisions.
Attempts have recently been made to more effectively treat these aqueous wastewater solutions so as to avoid the problems mentioned above. The focus of these attempts has been on the oxidation of the sulfur through the addition of highly reactive oxidizing agents, such as permanganates and peroxides. However, because of the highly reactive nature of these compounds, a serious potential exists for hazardous and explosive reactions.
Accordingly, there is a need for a process that is capable of effectively and efficiently treating these wastewater solutions so that all contaminants present are converted into a less-toxic state. Furthermore, a need also exists for a method of removing these contaminants as well as reducing the pH levels of such solutions.